linux-kernel - Re: [PATCH 0/4] CPUFreq statistics retrieved by drivers

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Date:   Wed, 5 Aug 2020 12:04:42 +0100
From:   Lukasz Luba <lukasz.luba@....com>
To:     Florian Fainelli <f.fainelli@...il.com>,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-pm@...r.kernel.org
Cc:     sudeep.holla@....com, cristian.marussi@....com,
        viresh.kumar@...aro.org, rjw@...ysocki.net
Subject: Re: [PATCH 0/4] CPUFreq statistics retrieved by drivers



On 8/4/20 6:27 PM, Florian Fainelli wrote:
> 
> 
> On 7/29/2020 8:12 AM, Lukasz Luba wrote:
>> Hi all,
>>
>> The existing CPUFreq framework does not tracks the statistics when the
>> 'fast switch' is used or when firmware changes the frequency independently
>> due to e.g. thermal reasons. However, the firmware might track the frequency
>> changes and expose this to the kernel.
> 
> Or the firmware might have changed the CPU frequency in response to a
> request from the secure world for instance.

Possible

> 
>>
>> This patch set aims to introduce CPUfreq statistics gathered by firmware
>> and retrieved by CPUFreq driver. It would require a new API functions
>> in the CPUFreq, which allows to poke drivers to get these stats.
> 
>  From a debugging perspective, it would be helpful if the firmware
> maintained statistics were exposed as a super-set of the Linux cpufreq
> statistics and aggregated into them such that you could view the normal
> world vs. secure world residency of a given frequency point. This would
> help because a lot of times, Linux requests freq X, but the secure world
> requires freq Y (with X >= Y) and people do not really understand why
> the resulting power usage is higher for instance.
> 
> What are your thoughts on this?
> 

I know that Viresh is going to develop patches and improve these
cpufreq stats framework. Maybe he also had this 'aggregation' in mind.
I will leave it him.

Thank you for your feedback.

Regards,
Lukasz